In industrial projects, valve quality is closely related to the manufacturing process. Even when valves use the same material standards, different manufacturing methods, such as forging, casting, extrusion and injection molding, will affect mechanical performance, dimensional accuracy, service life and applicable operating conditions. Understanding these processes helps engineers evaluate product quality more accurately and select suitable valves according to actual service requirements.
This article introduces the common manufacturing processes used for industrial valves, including forging, casting, brass extrusion forming, injection molding and machining. It also analyzes their characteristics, advantages and application scenarios based on actual manufacturing procedures for reference.
1. Main Types of Valve Manufacturing Processes
Valve manufacturing usually consists of two stages: blank forming and machining. The forming process determines the material structure, mechanical properties and service conditions of the valve, while machining determines sealing accuracy, assembly quality and dimensional consistency. Industrial valves mainly adopt four forming methods: forging, casting, brass hot extrusion (or hot forging), and injection molding. Each process corresponds to different materials, pressure ratings and application requirements.
1) Forging: A Common Manufacturing Method for High-Strength Valves
Forging forms metal blanks through plastic deformation under pressure after heating. It is mainly used for valve bodies and components that require high strength, toughness and fatigue resistance. Typical products include API 602 gate valves, globe valves, check valves, as well as power plant and high-pressure pipeline valves. Common materials include ASTM A105, A182 F304/F316, F11/F22 and other alloy steels.
2) Casting: A Common Manufacturing Method for Complex-Structure Valves
Casting can produce complex flow passages and medium-to-large valve bodies in a single forming process. It is widely used for gate valves, butterfly valves, globe valves and check valves. Since casting involves liquid metal solidification, manufacturers must carefully control defects such as shrinkage porosity, shrinkage cavities, gas porosity and element segregation. Under similar material grades and heat treatment conditions, cast valves generally have lower toughness and fatigue resistance than forged valves, but they provide better capability for complex geometry forming and large-diameter applications.
3) Extrusion Forming: A Common Material Forming Method for Brass Valves
During the manufacturing of brass ball valves, angle valves and some HVAC valves, brass materials are usually first produced into extruded bars, then cut, heated and processed through closed-die hot forging to form valve body blanks. This process is mainly applied to small and medium-sized brass valves, commonly ranging from DN15 to DN50. Some industrial brass or bronze valves can extend to DN80 or DN100. Typical pressure ratings include PN10, PN16 and PN25.
4) Injection Molding: A Manufacturing Method for Plastic Valves
Plastic valves made from PVC, CPVC, PP, PVDF and other materials are mainly produced through injection molding. Plastic pellets are heated and melted before being injected into molds, allowing valve bodies or valve covers to be formed in a single cycle. This process provides high production efficiency and is suitable for large-volume standardized products used in water treatment, chemical processing and irrigation systems.
5) Machining: A Critical Process for Ensuring Valve Dimensional Accuracy
Metal valves and some plastic valve components require additional machining after blank forming. CNC machining completes critical features such as sealing surfaces, flanges, threads and stem holes. The machining quality directly affects valve sealing performance, operating torque and assembly accuracy.
2. Forged Valve Manufacturing Process (Forged Valve Manufacturing)
Forged valves are mainly used in high-pressure, high-temperature and critical service applications. Compared with cast valves, forged valves provide higher material strength and better internal structure, making them widely used in oil and gas, power generation and chemical industries.
Valve Forging Heating
1) Basic Principle of Forged Valve Manufacturing
Forging applies pressure to metal blanks at high temperatures, causing plastic deformation instead of forming through melting and solidification. During the forging process, continuous metal fiber flow forms inside the material, reducing defects such as shrinkage cavities and porosity while improving strength, toughness and fatigue resistance.
2) Main Production Steps of Forged Valves
a) Material Cutting: Alloy bars are cut according to valve body specifications. The blank dimensions must remain consistent to prevent uneven loading and deformation during forging;
b) Controlled Heating: Different materials require different forging temperature ranges. For example, ASTM A105 forgings typically use an initial forging temperature of approximately 1150–1250℃, with a final forging temperature not lower than 850℃. For 304/316 stainless steel, the final forging temperature is generally maintained above 950℃. Infrared temperature monitoring is commonly used to prevent overheating or insufficient heating;
c) Pre-forging Forming: The material is initially shaped to optimize metal flow direction and reduce folding defects during final forging;
d) Final Forging and Sizing: The forging ratio directly affects the improvement of internal material structure. Based on common industrial control values, the total forging ratio for rolled bar forgings is usually maintained above approximately 1.5–2.0. For ingot or continuous casting billet forgings, the forging ratio is typically required to reach approximately 3.0 or higher to improve the core structure;
Valve forging processing
e) Controlled Cooling and Stabilization: The cooling method is selected according to the material hardenability tendency and forging cross-section. Options include air cooling, furnace cooling, sand cooling or insulated slow cooling. Small A105 carbon steel forgings can use controlled air cooling or slow cooling. Alloy steel forgings such as F11 and F22, as well as heavy-wall forgings, usually require stricter slow cooling procedures and subsequent heat treatment to reduce the risk of cold cracking and residual stress;
f) Heat Treatment: The heat treatment method is selected according to material grade, forging section size and mechanical property requirements. Available methods include annealing, normalizing, normalizing and tempering, or quenching and tempering. A105 carbon steel forgings commonly use normalizing or normalizing plus tempering, while F11 and F22 alloy steel forgings usually require normalizing and tempering or quenching and tempering;
g) Post-processing and Inspection: Shot blasting removes oxide scale, followed by MT or PT surface inspection according to product requirements. For petroleum, chemical, power generation, high-pressure or customer-specified projects, pressure-containing forgings may require 100% MT/PT inspection. General-purpose valves may use first-piece inspection, batch sampling inspection or focused inspection of critical areas.
3) Advantages of Forged Valves
a) Excellent Mechanical Properties: Forgings have refined grain structures and continuous metal fiber flow, providing superior tensile strength, fatigue resistance and impact resistance. Under cyclic loading conditions, forged valves generally achieve significantly longer service life than cast valves;
b) Better Defect Control: Forgings do not develop typical casting defects such as shrinkage cavities and shrinkage porosity during forming. They provide excellent pressure-bearing stability under high-pressure service conditions;
c) Wide Temperature Capability: By selecting suitable materials, forged valves can cover a wide operating temperature range. For example, austenitic stainless steel forgings can be used in LNG cryogenic applications at approximately −196℃, while chromium-molybdenum steel forgings such as F11 and F22 can be applied in high-temperature steam systems around 500–550℃;
d) Strong Compliance Capability: In applications requiring API, ASME and certain power plant standards, high-pressure valves are generally preferred in forged construction.
4) Limitations of Forged Valves
a) Limited Forming Capability: As valve size and individual component weight increase, forging pressure, die size and subsequent machining costs rise rapidly. For complex integral valve bodies above DN300, casting usually provides a clear economic advantage. Integral forged valve bodies of DN600 and above are relatively uncommon;
b) Higher Cost: Due to higher equipment, tooling, heat treatment and machining costs, forged steel valves are generally more expensive than cast steel valves with the same specifications;
c) Lower Material Utilization: Forgings require larger machining allowances, resulting in typical material utilization rates of approximately 60%–70%. For complex structures or products requiring extensive machining, the actual utilization rate may decrease further.
3. Cast Valve Manufacturing Process (Cast Valve Manufacturing)
Casting is one of the most widely used manufacturing processes for industrial valves, especially for complex structures, medium-to-large diameter valves and mass production valve bodies. With proper casting procedures and quality control, cast valves can meet most application requirements in industries such as oil, chemical processing, power generation and water treatment.
1) Basic Principle of Cast Valve Manufacturing
Casting pours molten metal into a mold cavity. After solidification, the formed valve body blank undergoes heat treatment, machining and inspection to become the finished product. Depending on product requirements, manufacturers may use sand casting, investment casting (lost-wax casting), shell molding and other processes.
Valve Casting Forming
2) Main Production Steps of Cast Valves
Industrial valve bodies commonly use resin sand casting and silica sol investment casting. Resin sand casting is mainly suitable for medium and large valve bodies, while investment casting is mainly used for smaller valve bodies requiring higher dimensional accuracy and surface quality.
a) Melting and Refining: Cast steel valve bodies can be produced using medium-frequency induction furnaces or electric arc furnaces. Important projects may add LF refining or VD vacuum degassing. For low-temperature steel, high-cleanliness stainless steel or special projects, manufacturers may control sulfur content below 0.015% and further reduce total oxygen content, with approximately 30 ppm used as an internal control target;
b) Mold Preparation: Sand casting uses sand molds and cores, while investment casting produces wax patterns, assembles tree clusters and applies multiple ceramic shell layers;
c) Pouring and Forming: Pouring temperatures vary depending on steel grade. For example, WCB cast steel is typically poured at approximately 1550–1600℃ to balance metal fluidity and solidification quality;
d) Cooling and Cleaning: Solidification, cooling and shakeout times are controlled according to material, wall thickness and casting weight. The process then continues with sand removal or shell removal, riser cutting, shot blasting and grinding;
Valve Casting Cooling
e) Heat Treatment: Heat treatment methods are selected according to material grade, including annealing, normalizing, normalizing and tempering, or solution treatment. WCB carbon steel valve bodies commonly use normalizing or normalizing plus tempering. CF8 and CF8M austenitic stainless steel valve bodies typically use solution treatment to improve microstructure and corrosion resistance;
f) Non-destructive Testing: Standard cast steel valve bodies normally undergo visual inspection, dimensional inspection and MT/PT surface testing. For high-pressure, low-temperature, heavy-wall or customer-specified projects, UT or RT internal inspection may also be required. Critical pressure-containing areas may receive 100% inspection, while standard batch products are inspected according to product standards, purchasing specifications or batch sampling plans.
3) Advantages of Cast Valves
a) Wide Forming Capability: Through investment casting, resin sand casting and large-scale sand casting processes, cast valve bodies can cover applications ranging from small valves around DN15 to large-diameter valves above DN2000. Complex flow paths and irregular internal cavities can be formed as an integrated structure without welded assembly;
b) High Cost Efficiency: Casting can directly form complex flow passages and reduce subsequent machining requirements. For mature mass-produced medium and large valve bodies, casting blank material utilization can reach approximately 70%–85%. Products with simple structures and high process yield may achieve even higher utilization. Compared with integral forged valve bodies, casting blank costs are typically 20%–50% lower;
c) Mature Manufacturing Process: Standardized mass production systems provide shorter delivery cycles and meet the requirements of municipal, general chemical, water supply and drainage applications.
4) Common Defects During Casting
Casting defects are mainly related to molten steel cleanliness, mold filling and solidification control. The presence of casting defects does not mean cast valves cannot be used in high-pressure applications. However, high-pressure, low-temperature and cyclic loading services usually require higher casting quality levels and additional RT, UT, MT or PT inspection to confirm that critical pressure-containing areas are free from unacceptable defects:
a) Shrinkage Porosity and Shrinkage Cavities: These are major internal defects controlled during cast steel valve production. They commonly occur at flange roots, thick-to-thin wall transition areas and other hot spots. If defects extend into the effective pressure-retaining wall thickness, they may reduce local load-bearing capacity and increase leakage or cracking risks under pressure cycling;
b) Element Segregation: Uneven distribution of alloying elements between the surface and core areas of the valve body can reduce local corrosion resistance and strength. Long-term operation may cause localized corrosion penetration;
c) Gas Porosity and Slag Inclusion: These defects are usually related to steel deoxidation, inclusion control, air entrainment during pouring and mold cavity ventilation. Isolated small pores may not directly cause failure. However, when defects are concentrated, located near sealing surfaces or appear in weak pressure areas, they may reduce effective wall thickness and become initiation points for fatigue cracks or corrosion propagation;
d) Coarse Grain Structure: Excessively high pouring temperature, slow cooling rate or improper heat treatment may cause grain coarsening, reducing impact toughness.
4. Application of Extrusion Process in Valve Manufacturing (Extrusion Process)
Extrusion forming forces a heated brass billet through a die under high pressure to produce a required cross-section or near-net-shape blank. During the entire process, the metal remains in a plastic state, allowing the material to achieve good structural density and mechanical properties.
1) Basic Principle of Extrusion Forming
A large number of brass ball valves, gate valves, angle valves and pipe fittings used in building water supply, HVAC and gas systems are manufactured using hot extrusion or hot-forged blanks, followed by CNC machining to complete the final products. Compared with direct casting, extruded bars provide better dimensional consistency, fewer internal defects and improved reliability for applications such as potable water and gas systems.
Valve Extrusion Forming
2) Application of Extrusion Process in Brass Valve Manufacturing
a) Billet Heating: According to the brass grade and bar specifications, brass billets are heated to the suitable temperature range required for extrusion forming;
b) High-Pressure Extrusion: The heated brass billet passes through the die under extrusion machine pressure to form bars, tubes or profiles with specified cross-sections. The typical extrusion ratio can be controlled around 4:1–8:1 depending on product cross-section and equipment capability;
c) Cooling and Straightening: Extruded materials undergo controlled cooling, followed by straightening, cutting to length and surface inspection;
d) Subsequent Cutting: According to valve body or component specifications, extruded bars are cut into blanks with required length or weight for subsequent forming or machining processes.
3) Advantages of Extrusion Forming
a) Excellent Performance: Without casting porosity defects, extruded valve bodies achieve density, vibration resistance and fatigue performance close to forged components and significantly better than cast copper valves;
b) Good Dimensional Consistency: Closed-die hot forging can produce stable near-net-shape blanks, although blank dimensions generally remain within millimeter-level tolerances;
c) Stable Mass Production: For mature production lines with stable tooling, bar materials and heating parameters, blank defects such as underfill, folding and cracking can usually be controlled at approximately 1% or lower.
4) Limitations of Extrusion Forming
a) Limited Diameter Range: Hot-forged brass valve bodies are mainly concentrated in DN15–DN50 applications, with some products extending to DN80 or DN100. As blank weight and projected area increase, the required forging force may rise from several hundred tons to several thousand tons. Even when large valve bodies are technically feasible, tooling, equipment and material costs often reduce economic efficiency.
b) Concentrated Material Application: This process is mainly used for brass, bronze and some aluminum alloy valves. Carbon steel and stainless steel can also be processed through extrusion to produce bars, tubes or special blanks. However, conventional industrial valve bodies more commonly use forging or casting rather than direct extrusion forming;
c) Operating Conditions Limited by Material Properties: The maximum operating temperature and pressure of brass valves depend on copper alloy strength, valve seat material and connection type. Standard brass ball valves are mainly used for water, air, gas and HVAC systems. They are not suitable for high-temperature steam, highly corrosive media or high-pressure petrochemical pipelines.
5. Application of Injection Molding in Plastic Valve Manufacturing (Injection Molding Process)
Plastic valves are widely used in water treatment, chemical processing, irrigation and swimming pool systems. Their manufacturing methods are completely different from metal valves. Most plastic valve bodies, valve covers and handles are produced through injection molding, providing high production efficiency and consistent product quality.
1) Basic Principle of Injection Molding
Injection molding heats thermoplastic materials such as PVC, CPVC, PP, PVDF and ABS until molten, then injects them into mold cavities under high pressure. After cooling and solidification, the final components are formed. For mass production, multi-cavity molds can continuously produce large quantities of identical parts, making injection molding the most mature manufacturing process for plastic valves.
Valve Injection Molding
2) Application of Injection Molding Process in Plastic Valve Production
a) Raw Material Preparation: PVDF and some engineering plastics usually require pre-drying according to supplier requirements. Typical drying time is approximately 2–4 hours. Whether PVC-U, PP and similar materials require drying depends on storage conditions, formulation and raw material condition. Moisture control values should follow the specific resin technical data sheet;
b) Multi-Stage Heating: Barrel temperature must be set according to each material. PVC-U normally requires lower and strictly controlled processing temperatures to prevent thermal degradation. PP processing temperatures are commonly around 180–230℃, while PVDF may require melt temperatures around 220–260℃;
c) Injection and Holding Pressure: Injection pressure must be adjusted according to flow length, wall thickness, gate design and material viscosity. Some hydraulic injection molding machines display system pressure values around 80–180 bar, while the converted actual plastic-side injection pressure can reach several hundred to over one thousand bar;
d) Cooling and Solidification: Mold temperature should also be set according to material characteristics. PVC-U and PP generally use relatively lower mold temperatures, while PVDF may require higher mold temperatures to improve surface quality and crystallization behavior;
e) Post-processing: Remove gates and flash, and perform annealing or natural aging when required. After valve assembly, shell strength and sealing tests are conducted according to product standards.
3) Advantages of Injection Molding
a) Excellent Corrosion Resistance: Different plastic materials can be applied to acids, alkalis, salts and other corrosive media. Among them, PVDF generally provides better chemical resistance and temperature capability than PVC-U and PP;
b) High Production Efficiency: Short molding cycles and multi-cavity molds significantly improve production capacity, making injection molding suitable for large-volume, cost-sensitive projects;
c) Extremely Low Material Waste: Under stable production conditions, injection molding can achieve effective material utilization rates of approximately 90%–98%. For certain clean water or general industrial products, clean recycled material of the same grade may be reused according to applicable requirements.
4) Limitations of Injection Molding
a) Lower Mechanical Strength: Plastic valve bodies generally have lower stiffness, impact resistance and long-term creep resistance than steel or copper valves. Therefore, they are more sensitive to pressure pulsation, water hammer, external pipe loads and installation stress;
b) Narrow Temperature and Pressure Range: PVC-U systems commonly operate at approximately 0–60℃. Many valves can reach PN10 or PN16 at 20℃, but allowable pressure decreases as temperature increases. PVDF systems can extend the temperature range to approximately −20–140℃. Some valves are rated PN10 or PN16 at 20℃. Excessive temperature or pressure may cause creep deformation or valve body cracking;
c) Clear Service Boundaries: Plastic valves are suitable for water treatment, chemical transfer, pure water, irrigation and certain gas pipelines. However, operation beyond the material pressure-temperature rating should be avoided, and water hammer, external loads and thermal expansion must be properly controlled.
6. Role of Machining in Valve Manufacturing (Machining Process)
For metal valves and some plastic valve components, machining is an essential step in the manufacturing process. It not only determines whether the product meets drawing requirements but also directly affects sealing performance, operating torque and assembly accuracy.
1) Precision Machining Process for Valve Bodies and Components
Valve bodies produced through forming processes always have dimensional deviations, surface roughness and insufficient precision for direct assembly. Standardized machining processes are required to complete final production. Taking a DN80 carbon steel valve body as an example, the typical machining sequence is as follows:
a) Reference Surface Rough Machining: The first step is to establish machining references on end faces, flanges or valve body mounting surfaces. For a DN80 medium and small carbon steel valve body, investment casting blanks may have machining allowances of approximately 1–3 mm per side, while sand casting blanks typically require approximately 3–6 mm or more;
b) Rough Turning and Forming: The main excess material is removed while maintaining approximately 0.3–0.8 mm machining allowance per side for finish machining. For welded sealing surfaces or thin-wall structures prone to deformation, additional allowance should be reserved according to subsequent heat input and deformation requirements;
c) Precision Finish Machining: Precision machining is performed on center flange sealing surfaces, valve stem packing areas and sealing bevel surfaces. After wear-resistant alloy overlay welding, secondary finishing is carried out;
d) Hole Machining: Standard flange holes, threads and stem grooves can be processed using vertical machining centers or dedicated machines. For complex valve bodies with multi-surface hole systems, inclined holes or reduced re-clamping requirements, four-axis, 3+2 axis or five-axis machining centers can be used to improve positional accuracy and consistency;
e) Precision Inspection: Coordinate measuring machines are used for full-dimensional verification, controlling concentricity, flatness and dimensional tolerances;
f) Final Treatment: Ultrasonic cleaning removes burrs, followed by rust prevention treatment to complete finished product machining.
Valve CNC Machining
2) How CNC Machining Ensures Dimensional Accuracy
CNC machining is the core method for controlling valve manufacturing accuracy. Through programmed and automated machining, it minimizes manual errors. The key accuracy control methods include:
a) Standardized Parameters: Cutting parameters should be determined according to material type, tool selection, cutting depth and machine rigidity. For example, when turning valve bodies with carbide tools, carbon steel rough machining feed rates may be approximately 0.20–0.50 mm/rev, while stainless steel finish machining may use approximately 0.05–0.20 mm/rev;
b) Standardized Machining Sequence: The process must follow the principles of “rough machining before finish machining, surfaces before holes, and reference surfaces first.” This gradually releases internal machining stress and prevents deformation after processing;
c) Equipment and Inspection Capability: High-precision machining centers can achieve axis positioning accuracy of approximately ±0.005–0.010 mm. Considering tool wear, clamping conditions, thermal deformation and blank stress, controlling critical valve body dimensions within ±0.02–0.05 mm is more practical for mass production;
d) Detailed Tool Control: Carbide tools should be dedicated to specific machining applications. Regular tool wear calibration is required to prevent accuracy deviations on sealing surfaces, threads and hole positions.
7. Differences Between Different Valve Manufacturing Processes
The following table compares four major blank forming processes and explains the role of machining in valve manufacturing. The comparison covers internal structure, typical defect levels, pressure and diameter ranges, manufacturing costs and application scenarios:
| Comparison Item | Forging Process | Casting Process | Brass Bar Extrusion + Hot Forging | Injection Molding Process | Machining |
| Internal Structure | Dense structure with relatively continuous metal flow; folding, cracking and inclusion defects still require control | Solidification structure with possible shrinkage porosity, gas pores and segregation | Extruded bar provides uniform structure, while hot-forged blanks achieve high density | Structure and crystallization state depend on resin type, temperature and cooling conditions | Does not change base material structure except local grinding or thermal processing |
| Main Quality Risks | Folding, cracking, abnormal fiber flow | Shrinkage porosity, gas pores, slag inclusion, segregation | Underfill, folding, hot cracking | Sink marks, bubbles, warpage, weld lines | Dimensional deviation, concentricity errors, unacceptable surface roughness |
| Mechanical Properties | Generally the highest under the same material conditions | Meets design requirements, but toughness and fatigue performance are usually lower than forgings | Brass valve body performance is generally better than cast copper blanks | Lower than metal valves and significantly affected by temperature and time | Determines dimensional accuracy, sealing and assembly performance |
| Common Pressure Range | Commonly Class 800, 1500 and 2500; not limited only to PN100 and above | Can cover Class 150–2500 depending on material, structure and quality level | Commonly PN10–PN25, some applications can reach PN40 or higher | Commonly PN10–PN16, requires temperature derating | Applicable to component machining under all pressure classes |
| Common Diameter Range | API 602 type valves are generally DN8–DN100; larger forgings are possible | DN15 to above DN2000 | Mainly DN15–DN50, some products extend to DN80/100 | Commonly DN15–DN300, depending on mold and product structure limitations | Covers all machinable valve sizes |
| Relative Manufacturing Cost | High | Medium to low, with clear advantages for large diameters | Medium | Lower for large-volume production, but initial tooling cost is high | Depends on machining complexity and tolerance requirements |
| Typical Applications | High-pressure, high-temperature, cryogenic and pressure fluctuation services | Large diameter, complex flow paths and general industrial systems | Water supply, gas, HVAC and refrigeration systems | Water treatment, chemical processing, pure water and irrigation | Manufacturing of all critical valve dimensions |
8. Summary
When selecting valves, engineers should consider manufacturing process, material standards, machining capability and quality control systems together. For critical engineering projects, the evaluation should also include pressure rating, service medium and certification requirements to comprehensively assess supplier manufacturing capability and quality consistency.
Different operating conditions require different manufacturing solutions. When evaluating forged valves, cast valves, brass valves or plastic valves, PLUMBERSTAR can provide suitable product recommendations and manufacturing solutions based on pressure class, service medium, material requirements and target market standards. This helps customers achieve a balance between quality, cost and delivery schedule. Please feel free to contact us for further support.
